Process of increasing the inductance of a loop antenna



Feb. 16, 1954 c, STELZER 2,669,528

PROCESS OF INCREASING THE INDUCTANCE OF A LOOP ANTENNA Original Filed May 11. 1950 azaam 2) E X INVENTOR.

Patented Feb. 16, 1954 2,669,528

UNITED STATES PATENT OFFICE PROCESS OF INCREASING THE INDUCT- ANC-E 0F A'LOOP ANTENNA Alphonse Charles Stelzer, Cincinnati, Ohio, as-

signor to Av'co Manufacturing Corporation, Cincinnati, Ohio, a corporation of Delaware Original application May 11, 1950, Serial No.

161,436. Divided and this application April 19,, 1951, ScriallNo. 221,891

1 Claim.- (Cl. 11 3 -37) '1 2 The present "invention is a division of my patwound by conventional machinery into the do} ent application Serial No. 161,436, filed May 11, sired loop configuration illustrated in Fig; 1, l 50, now Patent 2,602,891. each successive turn of the loop being located The present invention relates to loop antennas radially outwardly from the preceding one so and, without limiting the generality of the fore 3 that the thickness of the loop is that of the single going, particularly to the type employed in portconductor. The wire is suitably insulated as by able radio receivers and more specifically to a a thin plastic covering. novel loop antenna the L of which is critically Preparatory to the winding process a suitable predetermined, and tea novel process for making adhesive is applied to the conductor for purposes "the same, i of securing the adjacent loop turns together.

In many radio receivers in which a loop an- After drying the rigid loop is placed between tenn'a is included as 'a frequency determining two thin plastic Celluloid protective mounting parameter in the antenna input circuit, which members H and I2, each of which is slightly circuit is tunedasby agang capacitor iii-tracking larger than the loop in area and is formed with relationship to a local oscillator tank circuit, 1 a'generally' semicircular configuration to provide it is necessary to maintain the inductance (L) protective margins extending outwardly beyond of the loop antenna within very close tolerances. the periphery of the loop. Each of the mount.- In one well -kno'wn receiver of this type the first ing members is preformed with a plurality of tube following the antenna is a 'pentagrid conlarge apertures such as those indicated by the verter. A loop antenna para-lled "by a variable reference numerals l3, I4, I 5, and lfigior a pursection of "a gang condenser is R. coupled pose to be explained herehiaiter. Each of the between the third grid and cathode of this tube mounting members is also preformed with suitand an oscillator tank circuit, tuned by another able apertures to receive the terminal eyelets If! variable section of this gang condenser, and a and [8 to which the leads is and 20 are brought feedback coil are associated with "various ele'c- .15 out. The mounting members are also provided trodes of the tube in a known manner. The with preformed small apertures 2t, 22, 2'3, and 'two variable capacitor sections are ganged 'to- 24, whereby the loop assembly may be secured gether. In receivers of this and similar types to the lid of a portable radio receiver cabinet, it is necessary to maintain the predetermined for example, by conventional means. The as desired L-of'the loopwlthin'very close tolerances, 2o sembly of loop and dielectric mounting members and the present invention provides a novel-loop is secured together by strips of adhesive tape 25, in which this objective is achieved and a novel '25, 27 interlocking with notches 2'8, 29, and 3!) process for accomplishing it. formed on the mounting members. It will be An Object of the invention s o p v d 1 0p observed that the mounting members are idenantenna construction which pr i ly a d ri id y :1 ticaland the same die may be employedto punch adheres to a predetermined desired L characterthem out from the plastic dielectric material istic. of which they are made.

Another fundamentalobje'ct oi'theinvention is In practical commercial operations, as will-be to p d a novel pr ss f r djust n th L clearly understood by those skilled in the art, it =of-a'loop within a narrow range of tole in is customary'to manufacture the loop as a cornora bett r u d s d n of the present ihp'lete component. Before the loop is sent to the Ventibn, 'togther Wilih dfhel and further j assembly line .icr incorporation in a radio readvantas s, and apab lit es th r reference ceiver it is assumed that the inductance of the is made to th following d cription of the acloop falls within predetermined tolerances. In

companying d w n which there is Shown is receiving circuits in which the loop is a substan- & preferred illustrative form of loop antenna tial frequency-detgrminjng parameter it is nec.

made in accordance with the present invention. essary t i t i th inductance within very In the drawings: close tolerances. It will be appreciated that, ig. 1 is an illustration of a top View Of a 1001? once the loop I!) is formed, it would be a difllcult, antenna in accordance with the invention; cumbersome, expensive, and time-consuming op- Fig. 21s a front view thereof; and oration to add or to subtract turns or to re- Figs. 3 and 4 are sectional views taken on lines arrange the leads or to separate the loop from 3-3 and 44 of Fig. 1, looking in the direction the mounting assembly preparatory to final testof the arrows. ing of the loop and measurement of its in- The loop I0 is made of multistrand Litz wire ductance. Nonetheless, those are the expedients t able mounting members, the securing tape strips, the l end terminals, and the loop proper has been fabricated, the device is tested with a conventional L-meter. Various types of suitable inductance meters are well known. A conventional meter works on a resonance principle, and it comprises a fixed frequency oscillator having a load circuit, consisting of a variable capacitor,

calibrated in terms of inductance, and the -in' ductance under measurement. The variable capacitor is adjusted until resonance is attained, a peaking condition being indicated by an R. F. voltmeter. Since the resonant condition is a mathematical function of the inductance and capacitance parameters in the circuit, the fre- 'quency of the applied signal being constant, the capacitor can readily be calibrated in terms of inductance.

, Let it be assumed for purposes of discussion that the inductance of an assembly of this type, after measurement by an L-meter, is found to be too low. In accordance with the invention the operator continues to observe the indications of the meter while painting onto the loop a molten mixture comprising powdered ironand impregnating wax. It will be observed that sections of the loop are in registry with apertures l3, l4, 1 5, and I6, whereby access is permitted for that purpose. The application is made by theuse of an ordinary commercially available varnish or paint brush. The deposit of the metallic magnetic material increases the L of the loop, and the operator simply continues the brushing operation and the depositing of such material until the meter reading reaches the desired L value.

Although I do not desire to be limited to any specific proportions, or to any specific powdered magnetic material, satisfactory results have been achieved with a mixture of impregnating wax 'and iron powder, the proportion of the latter being 25% to 50% by volume, and the temperature of the molten mixture being maintained at 100 to 120 degrees centigrade, The iron powder has a tendency to settle to the bottomof the container, and it is desirable to immerse the applicator deeply therein or to agitate the mixture frequently. Any commercially available impregnating wax such as ceresine is entirely suit- Any suitable substance which will not destroy the insulation. on the loop conductor,

.which solidifies at ordinary temperatures encountered in operation and has a .low melting point may be used in lieu of the preferred wax.

.Any high permeability iron or ferromagnetic powder will serve as the powder component.

.Many suitable materials and alloys are known to the art. Low magnetic retentivity is desired.

The outstanding advantage of this process is that the ferromagnetic material which increases the inductnce of the loop is deposited in increments well within the control of a relatively unskilled operator, while the meter reading is observed so that there is no necessity to add or subtract turns or to disturb the loop leads or the mounting assembly in order to make the final adjustment to the desired inductance value. After deposition the molten mixture solidifies into durable masses 3!, 32 strongly adhering to the loop proper, and the assembly maintains the desired inductance characteristic throughout the usable life of commercially available radio receivers.

to keep the desired inductance value within or below the specified limits at the end of the winding operation, and special precautions aretaken to prevent those values from exceeding such limits. Therefore only those loops whichdo not conform to the specified inductance value are subjected to the process in accordance with-the invention, such process comprising a method for increasing the inductance of a loop.

While there has been shown and described what is at present regarded as the preferred embodiment of the invention, it will beunderstood by those skilled in the art that various modifications and substitutions of equivalents may be made therein without departing from the spirit and scope of the invention as defined by the claim hereto appended.

Having fully discussed and described my invention, I claim:

The process of increasing the inductance of a loop antenna of insulated wire to a predetermined inductance value which comprises detherethrough a ferromagnetic powder, permitting said hot melt to solidify, and thereafter sequentially measuring the inductance of the coated loop antenna and depositing additional increments of said hot melt at other separate and distinct preselected bare portions of said loop antenna until the desired predetermined inductance value is obtained, the total deposit of ferromagnetic powder being an amount suflicient to raise the inductance of the loop antenna to the desired predetermined value.

ALPHONSE CHARLES STELZER.-

References Cited in the file of this patent UNITED STATES PATENTS 

